Measurement Results for the Frequency-Tunable CMOS RF Power Amplifie - Linear CMOS RF Power Amplifiers for Wireless Applications - page 101

Fig. 7.1 Die photograph of
the stand-alone RF PA
7.2 Stand-Alone RF Power Amplifie Characterization
A stand-alone PA identical to the one used as the core of the frequency tunable RF
PA was designed and measured. Its schematic was already shown in Fig. 6.5 in the
previous chapter (refer to p. 84) and a die photograph is depicted in Fig. 7.1 .The
integrated components are the transistor ( M 1 ), the stability resistor ( R stab ) and ca-
pacitor ( C stab ), and the bias resistor ( R bias ). The matching networks, the DC blocks,
and the RF choke were placed off-chip on the printed-circuit evaluation board.
The PA chip was bonded to the board using the special procedure described in
Sect. 7.4 . Its input and output were connected to the ports of the network analyzer
through SMA connectors, coaxial bias tees, and coaxial cables. The bias tees were
used to provide gate (input) and drain (output) bias voltages for transistor M 1 as
well as DC blocks for the input and output.
The input and output matching networks were designed for a simultaneous con-
jugate match at 5.2 GHz using the procedure described in Chap. 10 (Appendix B).
The 2-port S parameters were measured with the network analyzer HP8719D [ 1 ]
calibrated from 1 to 6 GHz with the SOLT calibration kit [ 2 ] provided by the man-
ufacturer. The S parameters corresponding to the matched condition are shown in
Figs. 7.2 and 7.3 . It is worth stressing that this condition corresponds to a conju-
gate match at 5.2 GHz only, meaning that better matching could be achieved with
different matching networks at other frequencies.
Table 7.1 summarizes the S-parameter values for the PA matched for a 5.2 GHz
operation. Values at 2.4, 3.7, and 5.2 GHz are shown.
After that the PA was matched at 5.2 GHz, a 2-tone test was performed to mea-
sure the efficiency and linearity. Two tones centered at 5.2 GHz and spaced 500 kHz
apart from each other were applied. The input power was swept and the measured